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TOEIC Link Part 5 — whether vs if: Where the Two Overlap and the Four Places They Do Not

Part 5 tests whether and if as if they were interchangeable, but they are not — if is blocked before to-infinitives, after prepositions, in subject position, and before or not directly attached. This guide gives the one context where either works, the four contexts where only whether is legal, the whether...or structure, and worked items with the exact distractor logic TOEIC uses.

EnglishBlitz Editorial Team·

The committee has not decided ____ to approve the budget or defer it. The blank looks like it could take if — after all, whether and if both introduce yes/no clauses and the two are famously "interchangeable." But the correct answer here is whether, and if is not merely worse; it is ungrammatical. TOEIC exploits the belief that the two words are equal, because that belief is true in exactly one context and false in four. Once you know which is which, this item type becomes a structural check rather than a judgment call.

The one place either word works

Both whether and if can introduce a yes/no noun clause that is the object of a verb:

  • I don't know whether the shipment arrived.
  • I don't know if the shipment arrived.

Both are fine. This is the overlap zone, and it is the only one. Reporting verbs like know, ask, wonder, see, check, and confirm take either word when the clause sits directly after them. If the item you are looking at is this clean, whether and if will not both appear as options — TOEIC does not write items with two correct answers. So the presence of a whether/if choice is itself a signal: look for the structural feature that blocks if.

The four places only whether is legal

1. Before a to-infinitive

When the yes/no clause reduces to a to-infinitive, only whether survives:

  • Correct: They are deciding whether *to* renew the lease.
  • Wrong: They are deciding if to renew the lease.

if to does not exist in English. Any item with a bare to verb after the blank forces whether. This is the single most common trigger TOEIC uses for this item.

2. After a preposition

A yes/no clause that is the object of a preposition takes whether, never if:

  • Correct: The decision depends on *whether* the funding is approved.
  • Wrong: The decision depends on if the funding is approved.

Look for on, about, of, or as to immediately before the blank. This overlaps with the way embedded questions carry their own word order — the clause keeps statement order (subject before verb) regardless of which conjunction opens it.

3. In subject position

When the yes/no clause is the subject of the sentence, whether is required:

  • Correct: *Whether* the merger closes this quarter remains uncertain.
  • Wrong: If the merger closes this quarter remains uncertain.

Fronted if reads as a conditional ("if X, then...") and derails the parse. TOEIC plants this to catch candidates who default to if by habit.

4. Directly before or not

or not can attach right after whether, but not after if:

  • Correct: Please confirm *whether or not* you will attend.
  • Wrong: Please confirm if or not you will attend.

Note that if ... or not with the or not moved to the end is acceptable (confirm if you will attend or not), so the trap is specifically the adjacent or not.

The whether ... or structure

The opening item — decided ____ to approve the budget or defer it — combines two triggers: a to-infinitive and a later or. The whether ... or frame presents two alternatives, and if cannot host it. When you see a downstream or offering a second option, whether is almost always the answer. This is a noun-clause cousin of the choices in noun clauses and reported speech, where the clause keeps its internal statement order and the conjunction is chosen by the surrounding structure, not by meaning.

Worked items

  1. The report will indicate ____ the new supplier meets our quality standards.

    • Object of indicate, no blocking feature → either works, so TOEIC would pair whether with a distractor like that or what, not with if. If both appear, re-read for a hidden preposition or to.

  2. Management is still weighing ____ to expand into the regional market.

    • Bare to expand follows → whether. if is impossible before to.

  3. Success will hinge on ____ the pilot program reduces costs.

    • on immediately precedes the blank → whether. Preposition blocks if.

  4. ____ the applicants are qualified is for the panel to decide.

    • The clause is the subject of is → whether. Fronted if misreads as a conditional.

The one-question decision

When you see whether and if as competing options, do not ask "which sounds better." Ask a single structural question: is the clause anything other than the direct object of the verb? If it follows a preposition, precedes to, sits in subject position, or attaches to or not — the answer is whether, every time. Only when the clause is a clean verb object do the two overlap, and in that case TOEIC will have paired if or whether against a different distractor entirely. Reading for the blocking feature turns a "feels the same" item into a rule you can apply in three seconds.